This invention relates to a process for the liquefaction of carbonaceous solid fuels, particularly coals enhanced with respect to production of liquid carbonaceous fuels and solvents.
Many processes have been proposed for the production of low-sulfur, low-ash, carbonaceous fuels and distillate hydrocarbon fuels by solvent refining of coal in the presence of a hydrogen donor solvent. Typically, such a process includes the heating and liquefaction of the coal yielding light gases and a slurry which is further processed by vacuum distillation to produce a light distillate product, a recycle solvent, and a heavy fraction, including residual solvent, dissolved coal products, undissolved coal, minerals or ash materials, and unconverted coal macerals.
It is well known that further products may be produced by subjecting the vacuum still bottoms to a solvent deashing process which is sometimes referred to as "critical solvent deashing." Such a process is disclosed in U.S. Pat. No. 4,070,268. As indicated in that patent, the products of the critical solvent deashing process include a stream (HSRC) which is rich in coal products soluble in pyridine, but which is essentially free of ash and unconverted particulate coal. A bottom stream is also produced which includes insoluble coal products and ash. Finally, an underflow stream of LSRC rich in products soluble in benzene or toluene is produced which is either recycled as solvent in the SRC process or removed as a product.
As shown by U.S. Pat. No. 4,164,466, the solvent deashing stage often comprises several separation zones, each maintained at successively higher temperatures and at high pressure. This patent also discloses a process wherein the underflow stream of the second zone in the deashing stage is recycled to the entry mixing zone in the deashing stage.
In the process disclosed in U.S. Pat. No. 4,189,372, a portion of the underflow from the third and fourth separators is hydrogenated and recycled to the coal liquefaction slurry tank. Substantially all other intermediate streams from the second through the fourth separators are recycled to the entry mixing zone of the SRC process stage as in the U.S. Pat. No. 4,164,466.
In U.S. Pat. No. 4,119,523, the underflow from the first separator in the solvent deashing stage is extracted to separate the resulting ash and undissolved coal, and the remaining extract recycled to the coal liquefaction stage.
U.S. Pat. No. 4,298,451 teaches the catalytic hydrocracking of a clean coal extract 500.degree. F.+ (260.degree. C.+). The process disclosed uses a catalytic ebullated bed hydrocracker maintained at a temperature of 750.degree.-825.degree. F. (399.degree.-441.degree. C.) and a hydrogen pressure of 2000-3000 psi (13793-20689 Kpa). The preferred catalyst is NiMo.
U.S. Pat. No. 4,111,788 teaches the hydrogenation of the total effluent of a non-catalytic first stage reaction in an ebullated bed catalytic reaction zone which consists of two reactors. The first reactor may comprise an ebullated bed of non-catalytic material while the second zone is an ebullated bed of catalyst.
U.S. Pat. No. 4,255,248 discloses a two-stage process for the catalytic hydrocracking of coal in which the first stage comprises a catalytic reactor operating under hydrocracking conditions.
In view of this prior art there remains a need for further varieties of products and enhancements to an integrated two-stage coal liquefaction process.
It is, therefore, the general object of the present invention to provide such products and improved processes.